Cestodes are generally flat, segmented and ribbon-like worms, and are commonly known as tapeworms. They have no mouth or digestive system and so absorb nutrients across the body wall (cuticle).
All members of this class are parasitic.
Characteristics of Cestodes (Tape worm)
A chain of reproductive units called strobilla with scolex (hold fast organ) attached to the intestinal wall
Scolex has suckers and rostellum. Scolex is armed (with hooks) or unarmed (without hooks)
No organs of prehension or digestion. Nutrients absorbed through specialised integument (body wall / skin)
Flat shape affords maximum absorption of nutrients
Taenia saginata (human tapeworm: contain about 2,000 segments and is around 3.6 metre long); Echincoccus granulosus ( just about 2 to 8mmlength)
Both sexes in the same individual
Some segments have uterine pore for escape of eggs
Those without the pores, segments detach when they become mature ( gravid)
Either eggs or the segments are found in the faeces ( starts appearing in faeces six
to eight weeks after ingestion of cysticercus
Require intermediate hosts to complete lifecycle
1st stage larva called as oncosphere containing hexacanth embryo
2nd stage larvae (cysticercoid) fluid filled bladder with one or more scolices (bladder worm)
The body is divided into the scolex, neck and proglottids
The scolex (head): The scolex is usually modified with hooks and/or suckers which fasten to the host gut wall and provide an anchor to prevent removal of the worm by host bowel activity.
The neck: The neck is an unsegmented region of high regenerative capacity. If treatment fails to eliminate the neck and scolex, the entire worm may regenerate.
Proglottids (segments): The body is divided into sections called proglottids. Proglottids closest to the neck are undifferentiated. As proglottids move caudally, each develops hermaphroditic sex organs. Distal proglottids are gravid and contain eggs in a uterus. The mature proglottids, gravid with eggs, detach and are voided with the host feces.
Different segments of tapeworm
The life cycle is often complex and involves intermediate hosts. All cestodes cycle pass through 3 stages—eggs, larvae, and adults. Adults inhabit the intestines of definitive hosts, mammalian carnivores. Several of the adult tapeworms that infect humans are named after their intermediate host:
The fish tapeworm (Diphyllobothrium latum),
The beef tapeworm (Taenia saginata), and
The pork tapeworm (Taenia solium).
Eggs are excreted with faeces into the environment and ingested by an intermediate host (typically another species) in which larvae develop, enter the circulation, and encyst in the musculature or other organs. When the intermediate host is eaten, cysts develop into adult tapeworms in the intestines of the definitive host, restarting the cycle. With some cestode species (e.g., T. solium), the definitive host can also serve as an intermediate host and develop tissue cysts instead of intestinal worms if eggs are ingested.
Life Cycle of Tapeworm
Although adult tapeworms do cause disease, it is the cystic forms in intermediate hosts that are of great overall veterinary and public health importance. These can cause severe and even lethal disease, most importantly in the brain, but also in the liver, lungs, eyes, muscles, and subcutaneous tissues.
In humans, T. solium causes cysticercosis, and Echinococcus granulosus and E. multilocularis cause hydatid disease. Sparganum mansoni and T. multiceps larvae also can infect humans
Thus, some species live in the intestines of dogs and cause no detectable harm to them, but can grow into football-sized cysts in the liver and lungs of other hosts as humans who are unfortunate enough to ingest the eggs. Ingestion of cysts in meat and fish can also cause disease in humans, ranging from the benign to the life-threatening depending on the tapeworm species involved.
Adult tapeworms in the intestine have also been associated with intestinal upsets and anaemia in humans, and colic in horses.
Symptoms, Signs, and Diagnosis
Adult tapeworms are so well adapted to their hosts that they cause minimal symptoms. Larvae, however, may elicit intense immunologic reactions as they travel through tissues (hence inducing immunity) and cause severe disease when they settle in extra-intestinal sites.
Adult tapeworm infections are diagnosed by identifying eggs or gravid proglottid segments in stool. Larval disease is best identified by imaging studies, such as brain CT scan or MRI scan, and for some species, serologic tests.
Treatment and Prevention
The anthelmintic agents, praziquantel and niclosamide, are effective for most intestinal tapeworm infections.
Praziquantel @ 1 mg/kg BW in horses
@ 3.75 mg/kg in sheep
@ 5 mg/ kg in dogs and cats
Some extra intestinal infections respond to anthelmintic treatment, whereas others require surgical intervention.
Prevention and control
Thorough cooking (to temperature > 57° C [> 135° F]) of pork, beef, lamb, game meat, and fish;
Regular worming of dogs and cats;
Preventing recycling through hosts, such as dogs eating dead carcasses reduction and avoidance of intermediate hosts such as rodents, fleas, and grain beetles;
Meat inspection; and
Sanitary treatment of human waste
Prolonged freezing of meat is effective, pickling is variably effective, and smoking and drying are ineffective.
Taeniidae: Taenia solium (cysticercus) ,T.saginata, T.ovis, T.multiceps (coenurus), T.hydatigena, Echinococcus granulosus (hydatid)
Anoplocephalidae: Moniezia expansa, M.benedeni
Genus: Diphylobothrium: Species - D.latum (infection in man from fish)
Genus: Spirometra: Species – S.mansonoides (definitive host cats)
This parasite has a cosmopolitan distribution, with estimates of approximately 50 million cases of infection world-wide annually. This parasite has pigs as the main intermediate host, but man may also act as an intermediate host for this parasite as well as being infected with the adult tapeworms.
Larvae - These small cysticerci (referred to as Cysticercus cellulosae) found in the muscles or subcutaneous tissues (the normal sites for the larval of this parasite) may be found in other tissues such as central nervous system where they may grow much larger, up to several cm in diameter.
Adults - The adult tapeworms have an average length of ~ 3 meters, but may grow up to 8 meters in length occasionally. The scolex is equipped with a low rostellum with a double crown of approximately 30 hooks.
Pathology of Infection
Larvae - the annual world-wide mortality due to cysticercosis has been estimated at approximately 50 000 cases. Cysticerci mainly develop in the subcutaneous tissues, infections in both the CNS and ocular tissues also very common. Ocular infection can cause discomfort and can later bring about detachment of the retina.
Pigs usually do not show signs of infection. Cysticerci infection (commonly referred to as measly pork or pork measles) is usually only found when the meat is inspected.
Food, water or soil may become contaminated with tapeworm eggs from human feces. Prevent exposure by:
-cooking pork thoroughly (56°C)
-washing hands frequently when preparing food
-using clean utensils to prevent cross-contamination during food processing
-inspection of beef/pork for cysticerci
-Freezing at -10°C for 10 days
Taenia multiceps, The Coenurus Tapeworm
The adult worm is found in dogs or wild canids.
The larva is a bladderworm with multiple scoleces, called a coenurus.
The usual intermediate host is the sheep.
Treatment is chiefly surgical, although the drugs used for cysticercosis may also be effective against coenurus infection
Echinococcosis (hydatid disease) can develop in any tissue site, including the liver, lungs, heart, brain, kidneys, and long bones.
The clinical manifestations depend on the site and size of the cyst, but resemble those of a slow-growing tumor that causes gradually increasing pressure.
Infection of dogs and cats
Fleas are the intermediate hosts
Diphyllobothrium latum (The broad fish tapeworm)
Infection with Diphyllobothrium latum is usually asymptomatic, although occasional diarrhea, abdominal pain, fatigue, vomiting, dizziness, or numbness of fingers and toes may be present. Eosinophilia develops during the early stages of worm growth
Tapeworm of cattle and other ruminants
Monezia (Monezia expansa and M.benedini)
The adult tapeworms are about 600 cm long with no rostellum and hooks. Eggs of M.expansa are triangular-shaped while that of M.benedini square- shaped
Definitive host: Ruminants Intermediate host: Orbatid mites. The larva stage is called as cysticercoid.
Highly pathogenic in young animals, especially lambs
Fecal sample examination
Praziquantel @ 15 mg/kg
Albendazole @ 10 mg/kg
Control mites in pasture by ploughing
Other parasites of ruminants
Avitallina lahorea: DH: sheep and other ruminants (Small intestine) IH: Lice
Stilezia hepatica: DH: Ruminants (bile ducts)
Thysamosoma actinoides: DH: Ruminants (Bile ducts, small intestine, pancreatic duct)
Tapeworm of equines
Anaplocephala perfoliata: DH: equines (Large and small intestines)
A.magna: DH: equines (stomach and small intestine)
IH: Orbatid mites
Pathogenesis and clinical signs
Large number of parasites in intestine resuslts in weakness, cachexia, anaemia. Heavy infestation can lead to death of the animal.
Tapeworm of birds
Davainea proglottina: found in the duodenum of birds
They are armed with hammer-shaped hooks
Rallietina tetragona: found in the small intestine of birds. IH: ants
R.echinobothrida: small intestine of chikens and turkeys IH: ants
Cotugnia diagnophora: Small intestine of birds
Amoebotaenia sphenoides: small intestine of fowls. Rose-thorn shaped hooks
Pathogenesis of tapeworms in birds
R.echinobothrida causes nodule formation at the site of attachment severe enteritis
D.proglottina bury deep in the intestinal villi haemorrhage, necrosis and desesntry
Retarded growth in young and reduced production in adults
Loss of condition, emaciation, anaemia
Partial or complete paralysis
Gravid segments in feces, clinical signs and postmortem examination
Niclosamide @ 22 mg/kg
Albendazole, Oxybendazole and praziquantel
The control measures are directed at the control of intermediate hosts. Insecticides can be used for the control of intermediate hosts.
Regular deworming of birds